LAUSR

Abstract The present work investigated the influence of SiO 2 and ZrO 2 incorporated nanoparticles on the coating structure and the corrosion behavior of 6061 Al alloy coated by plasma electrolytic oxidation (PEO). To achieve this purpose, a set of PEO treatments were conducted in alternating current condition at a constant current density of 130 mAcm −2 in phosphate electrolytes containing each and both nanoparticles, respectively. Microstructure observations revealed that when SiO 2 or/and ZrO 2 nanoparticles were added to the electrolyte, both size and fraction of micropores tended to be decreased, which would be attributed to the incorporation of nanoparticles. SiO 2 nanoparticles were preferentially embedded in the vicinity of micropores, meanwhile ZrO 2 nanoparticles preferentially filled the cracks. m -ZrO 2 was mostly converted to o -ZrO 2 while SiO 2 were partly converted to o -SiO 2 and another part to mullite. Based on potentiodynamic polarization tests in 3.5 wt% NaCl solution, the coatings containing both SiO 2 and ZrO 2 nanoparticles exhibited excellent corrosion protection properties due to the combination of their roles as the micropores blocker and cracks filler so that the microstructural defects were minimized.